7.1Introduction
Xanthones are polyphenol compounds found in some higher plant families, fungi, and lichens (Negi et al. 2013). All xanthones possess the same oxygen–heterocycle backbone formed by a γ-pyron moiety condensed with two benzene rings (C6–C1–C6) known as xanthone, xanthene-9-one, or dibenzo-γ-pyrone. This symmetric chemical structure makes the xanthone a very stable molecule (Figure 7.1; Pedraza-Chavarri et al. 2008).
Figure 7.1Xanthone backbone chemical structure.
Xanthones were first discovered and isolated in 1855 from pericarp of mangosteen fruit (Garcinia mangostana L.) by a German scientist performing research on dysentery. α-Mangostin was found among the major xanthones taken from the pericarps of mangosteen fruit (Figure 7.2) (Schmid 1855). It is a yellow-colored matter, and for that reason, these compounds were named xanthones from the Greek word for yellow, xanthos. α-Mangostin can be obtained from other parts of the plant, such as the dried sap, leaves, bark, seeds, and whole fruit. Later, the α-mangostin structure was elucidated (Dragendorff 1930; Murakami 1932) and the molecular formula and type and position of substituents of α-mangostin was established (Yates and Stout 1958; Figure 7.2). It has been discovered that the compound possesses a wide range of biological activities, such as anti-inflammatory, antitumor, antioxidant, cardioprotective, antidiabetic, antiobesity, antifungal, antiparasitic, antiviral, antiallergy, and antibacterial (Gutierrez-Orozco and Failla 2013; Ibrahim et al. 2016).
Figure 7.2Chemical structures of the most abundant xanthones in mangosteen fruit (Garcinia mangostana L.).
The biological activities of xanthones are associated with their tricycle structure but vary depending on the nature or position of the different substituents, such as isoprene, methoxyl, and hydroxyl groups located at various positions of the A and B rings (Pedraza-Chavarri et al. 2008). Xanthones have been classified into five groups: (1) simple oxygenated xanthones, (2) xanthone glycosides, (3) prenylated xanthones, (4) xanthololignoids, and (5) miscellaneous xanthones (Negi et al. 2013).
In general, xanthones are biologically active polyphenolic compounds structurally very similar to flavonoids; their chromatographic behavior is also similar. Although flavonoids are frequently encountered in plant nature, xanthones are found in a limited number of families, such as Gentianaceae, Guttiferae, Moraceae, Clusiaceae, and Polygalaceae. The types, isolation, characterization, and biological applications of naturally occurring xanthones have been widely studied and reviewed (Obolsky et al. 2009; Negi et al. 2013; Gutierrez-Orozco and Failla 2013; Ibrahim et al. 2016). Naturally occurring xanthones have emerged as an important phytochemical in view of their remarkable pharmacological and other biological activities. It has been found that many plant products regularly used in traditional medicine as therapeutic agents contain xanthones as active constituents (Pinto et al. 2005; Na 2009; El-Seedi et al. 2010; Panda et al. 2013). In recent years, many chemical and pharmacological studies have been carried out to reveal a range of bioactivities of plants of the genus Garcinia (Gentianaceae family), such as anti-inflamation, antioxidation, anti-adipogenesis, anticancer, antimicrobial, anti-HIV, anticonvulsant, and antimalarial agents (Gutierrez-Orozco and Failla 2013; Jindarat 2014; Ibrahim et al. 2016). The pharmacological importance of xanthones have encouraged sc...
